Charles J. Goodacre

A method for assessing the clinical solubility and disintegration of luting cements

A test was designed for evaluating the distintegration of cementing agents in the oral cavity. The cements were placed in small holes located in the proximal surfaces of cast gold restorations so that the materials were not subject to abrasion. Each cement was placed in one hole located occlusally and one located gingivally. Four commercial cements of four different types (zinc phosphate, zinc silicophosphate, polycarboxylate, and EBA-Alumina zinc oxide/eugenol) were tested in 15 patients, and differences were observed in the deterioration rates of the different cements over the 6 month period. The disintegration rate of a given cement was the same in the gingival and occlusal positions. No correlation was observed between the clinical data on loss of material and the solubility of the cements as measured by conventional in vitro tests.

Palladium-silver alloys: A review of the literature

Since their introduction in 1973, the use of palladium-silver alloys has increased significantly and they now comprise a substantial part of the noble metal ceramic alloy sales in North America. Literature regarding various properties of this alloy system is presented with particular emphasis on castability, fit, and porcelain discoloration.

Microleakage and shear bond strength of resin and porcelain veneers bonded to cast alloys

Four resin veneering materials and four methods of retaining the veneer on metal castings were compared with metal ceramic restoration. Variations in microleakage were noted between the four resin materials retained by mechanical retention beads. When mechanical and chemical modes of a resin and porcelain veneer retention were compared, there was no microleakage with one mechanically and two chemically retained resin groups including one metal ceramic group. The resin materials tested understandably produced substantially lower shear bond strengths than the metal ceramic specimens. Higher shear bond strengths were recorded for the retentive beads than for the resins retained by three chemical bonding techniques. There was no direct correlation between microleakage and shear bond strength.

A comparative study of the strength of aluminous porcelain jacket crowns constructed with the conventional and twin foil technique

The purpose of this study was to evaluate and compare the strength of aluminous porcelain jacket crowns made in the following manners: (1) the conventional technique, (2) the conventional technique with a pure alumina insert, (3) the twin foil technique, and (4) the twin foil technique with a pure alumina insert. The conclusions of this investigation can be summarized as follows: 1. Porosity was observed in all the restorations made by each of the techniques. 2. The porosity was greater at the porcelain-platinum foil interface than anywhere else throughout the restoration with both the conventional and twin foil techniques. 3. The porosity seemed to be evenly distributed along the interface, with no concentration in any area. 4. Regardless of the technique, crowns that were more porous fractured at lower values. 5. Crowns built by the twin foil technique were significantly more porous at the interface of the tin-plated platinum and the porcelain core than those built by the conventional technique. 6. Crowns constructed with the conventional technique were significantly stronger than those constructed with the twin foil technique. 7. There was no bond between the core porcelain and the platinum foil matrix in crowns constructed by the conventional technique. 8. There seemed to be a strong bond between the core porcelain and the tin-plated platinum matrix in crowns built by the twin foil technique. 9. The presence or absence of the alumina insert on crowns constructed with the conventional and twin foil technique did not affect the strength of the crowns when tested at the incisal edge.

A comparison of the physical properties of four prosthetic veneering materials

Four resin materials used to veneer metal castings were compared by evaluating certain physical properties. Three of the materials were microfilled resins and one was an unfilled resin. Although no material proved to be superior in all of the tests, the microfilled materials were generally better than the unfilled materials. The heat- and pressure- polymerized microfilled material was inferior to the two light-polymerized microfilled materials in three of the physical property tests, superior to them in one test, and proved to be equivalent to them in two tests.

A comparison of condylar control settings obtained from wax interocclusal records and simplified mandibular motion analyzers

S cmiadjustable articulators that possess preformed condylar controls based on averages from clinical data have recently become available. The controls are set by recording data from simplified mandibular motion analyzers that record immediate side-shift and protrusive condylar pathways. The purpose of this study was to compare articulator condylar control settings obtained from wax interocclusal records with two different simplified analyzers.

Recent graduates' and current dental students' evaluation of their prosthodontic curriculum

This survey of recent graduates and third- and fourth-year dental students at Indiana University School of Dentistry determined whether the prosthodontic curriculum adequately prepared students for the prosthodontic portion of dental practice and whether there was material that should be added to or omitted from the prosthodontic curriculum. The survey evaluated 106 topics in the prosthodontic curriculum and areas related to prosthodontics. On the basis of their importance to the respondents, 59.4% of the topics were considered adequately emphasized, 2.9% of the topics were overemphasized and should be reduced in emphasis or eliminated, and 37.7% of the topics were underemphasized, which indicated the need to increase time devoted to these topics. Most of the underemphasized topics dealt with new materials, alternate techniques, private practice and its management, and the prosthodontic needs of special types of patients.

A comparison of the strength of base metal and gold solder joints

The purpose of this study was to evaluate the procedures involved in forming high- and low-fusing solder joints between two different base metal alloys and to compare the strength of these joints with the strength of those formed between specimens made from a high-gold content alloy. The conclusions of this investigation can be summarized as follows. All but 11 of the 120 specimens failed through the solder joint, which confirms that the solder joint is usually the weakest part of a fixed partial denture. The high-fusing joints formed between the base metal alloys showed higher relative bending strength values than the high-fusing joints formed between the gold alloy specimens. The low-fusing joints formed between the base metal alloys showed higher relative bending strength values than the low-fusing joints formed between the gold alloy specimens, and the low-fusing base metal joints exhibited the highest strength values in this study. The low-fusing joints formed between gold alloy specimens consistently bent before fracturing. Solder joints fail both adhesively (separation of the solder from the parent metal) and cohesively (fracture through the solder, parent metal, or a combination of both). A correctly formed joint between gold components should show cohesive fracture, whereas adhesive fractures are apparently acceptable with base metal alloys since the low-fusing base metal joints failed in this manner but still exhibited high strength values. Voids of different sizes and locations were observed in most of the solder joints, and within each group tested there was usually less strength exhibited by the joints with larger areas of porosity.

Effect of two opaquing techniques and two metal surface conditions on metal-ceramic bond strength

The optimal conditions for opaquing techniques during porcelain application have not been confirmed. In this study the metal-ceramic bond strength was measured among one porcelain and three dental alloys, namely a gold-platinum-palladium alloy, a silver-free gold-palladium alloy, and a base metal alloy, with two opaquing techniques (a single masking layer versus a thin overfired layer followed by a second masking layer). In addition, the opaque porcelain was fired over an oxidized and nonoxidized alloy surface for the silver-free gold-palladium alloy. No significant differences in bond strength were recorded between the two opaquing techniques with the gold-platinum-palladium and base metal alloys. There was no substantial differences between the two opaquing techniques when opaque was applied over an oxidized gold-palladium alloy surface and bond strengths were substantially greater over an oxidized surface. However, when the opaque was applied to a nonoxidized gold-palladium surface the two-layer technique created a significantly greater bond strength.

Eliminating coronal discoloration when cementing all-ceramic restorations over metal posts and cores

Opaque procelain was fused over metal posts and cores. This procedure permitted the definitive all-ceramic restorations to possess a more uniform shade between teeth restored with metal posts and cores and adjacent vital teeth.